During the usage of a turbine reduction gearbox, sometimes, oil leakage may be caused by defects such as the presence of sand holes, fine cracks and the like on the gearbox body or by insufficient tightness of the cover. In order to avoid the potential oil leakage of a turbine reduction gearbox during the operation, it is desired to perform an air-tightness test on the turbine reduction gearbox. In order to test the air-tightness of a turbine reduction gearbox, testers usually tests the air-tightness of the turbine reduction gearbox by immersing it in water. However, since whether the gearbox is tight or not depends upon a long period of observation by the testers, the automatic testing cannot be realized, and the labor intensity of the testers is increased. Sometimes, a component under test may be mistakenly regarded as qualified when bubbles are adsorbed on the bottom of the turbine reduction gearbox. Furthermore, immersing in water may cause adverse effects, for example, rusting of irony members such as worm wheels and worms.